1. Field of the Invention
The present invention relates to an image forming apparatus having document conveying means for conveying a document to a predetermined read position. More particularly, the present invention relates to a silent image forming apparatus in which document conveying means can operate with reduced operating noise during a document reading process in a standby state.
2. Description of Related Art
Some conventional image forming apparatuses, e.g., copying machines have an automatic document feeder provided as a means for conveying a document to be read to a predetermined read position. In such image forming apparatuses, a document to be copied is first placed on a document tray of the document feeder and is then conveyed automatically to the position on a platen glass, followed by reading of the document image with reading means.
In recent years, copying machines such as digital copying machines and digital combination machines having functions corresponding to the functions of a copying machine, a facsimile machine and a printer have come on the scene. Such copying machines include a type using a procedure for improving the productivity as described below. During standby before the temperature of a fixing device of the copying machine is increased to a predetermined (fixing) temperature, a document is read before a copying operation and document information obtained by reading the document is stored in a memory to enable the copying operation to be started immediately after the standby state.
On the other hand, automatic document feeders provided in such copying machines include a type designed so as to achieve a space saving effect as well as an improvement in productivity, for example, in such a manner that, while information written on a document separated and taken up from a top of a batch of documents is being read by reading means, a preceding document can be independently discharged in a reversed state.
Further, copying machines having such an automatic document feeder include a machine designed so as to achieve an improvement in productivity and matching with an arrangement relating to discharge of a top page from a printing unit in such a manner that copy output sheets are discharged by reversing discharge (discharge of sheets with the back surface up) in order in correspondence with the order of documents from the first page.
With respect to the above-described conventional copying machines (image forming apparatus), it has been pointed out that, in a case where a copying machine arranged as described above is placed in a quiet office, a user may have a feeling of discomfort due to operating noise caused during standby by the above-described operation for reading a document before a start of a copying operation.
In a case where an arrangement enabling independent reversing discharge of a preceding document is adopted for the purpose of achieving a space saving effect and improving the productivity of a copying machine, the document reversing discharge operation and the discharge operation of a copying machine main unit are performed substantially in synchronization with each other. In this case, therefore, the operating noise caused by the operation of the entire system formed of the copying machine main unit and the automatic document feeder in combination is increased.
The conveying speed for the reversing discharge operation selected to ensure increased productivity is about twice as high as feeding speed and the conveying speed during times other than when the reversing discharge operation is performed. Therefore the operating noise problem with the conveying speed for the reversing discharge operation is particularly serious and the resulting influence on users in a quiet office environment is considerable and there has been a demand for a solution to the problem.